Concentration process for plutonium ions, in an oxidation state not greater than +4, in aqueous acid solution



Patented June 14, 1960 2,940,819- CONCENTRATION PROCESS. non PLUTONIUM IONS, IN AN OXIDATION STATE NOT GREATER THAN +4, INAQUEOUS ACID SOLUTION No Drawing. Filed Sept. 20, 1946, Ser. No. 698,410 5 Claims. (Cl. 23-145 The present invention relates to an improved process for the recovery, concentration, and decontaminauon of certain transuranic elements from their solutions. More particularly, it pertains to a method for the recovery, concentration, and decontamination of plutonium from solutions thereof by the utilization of a single carrier or a combination of such carriers therefor and to the new and useful compounds produced by such method.

The term element 94 is used throughout this description to designate the element having atomic number 94. The designation 94 refers to the isotopeof element 94 having a mass number of 239. Element 94 is also referred to herein as plutonium, symbol Pu. Likewise, element 93 means the element having atomic number 93, which is also referred to as neptunium, symbol Np. Referenceherein to any of the elements is to be understood as denoting the element generically, whether in its free state, or in the form of a compound, unless otherwise indicated by the context.

The apparent discovery of transuranic elements (e1ement 93 and elements of higher number) was first announced by E. Fermi in 1934. At that time Fermi stated that the bombardment of uranium with neutrons gave beta activities which he attributed to transuranic elements of atomic number 93 and possibly higher. From 1934 to 1938 other workers, notably Hahn and Curie, extended this work. But in 1939, Hahn discovered that the elements which he and others had believedto be transuranie elements were in fact radioactive elements of medium atomic weight produced by the fission of uranium. Hahns results were subsequently confirmed, and a great many fission products in addition to those first found by Hahn were discovered and identified. Such products were all of lower atomic number than uranium, generally of atomic numbers inthemiddle of the periodic group; and so far as is known, prior to about June. 1940, no positive evidence was found to establish the existence of any transuranic element.

However, in June 1940, McMillan and Abelson published in The Physical Review, 57, 1185, their discovery that a 2.3 day activity produced by the bombardment of uranium with neutrons was an isotope of element 93, probably 93 Although McMillan and Abelson surmised that element 94 would be formed by beta decay of element 93 they were unable to produce any positive evidence of its existence, and did not obtain either 93 9 or 94 in pure form or in macroscopic amounts, either as the element or as a compound.

Subsequently, G. T. Seaborg and associates obtaining 93 admixed with rare earths, proved that 93 decayed to 94 and measured the radioactive and fission properties of 94 Thereafter, neutronic reactors were developed for the production of 93 and 94 in iso- Thompson,

. 2 latable quantities by a self-sustaining. chain reaction of slow neutrons with U .and U in natural uranium, I

-Natural uranium comprises largely isotope U 9 together with about as much U 5 and a very much smaller amount of U When this mixtureof isotopes either as metallic uraniumor as a uranium;compound,

is subjected to bombardment by neutrons, or undergoes a self-sustaining neutronic chain reaction, a number of nuclear reactions takes place. Isotope U3 captures neutrons to form U which undergoes beta decay to form transuranic elements in the following manner:

' 23 min. (13-) 2.3 days (B {11384. U210 Isotope U undergoes fission, i.e., a breakdown of its heavy nucleus into lighter fragments which are generally very unstable and highly radioactive. Such fragments usually undergo beta-particle disintegration in successive steps, leading ultimately to stable isotopes of higher nuclear charge than the original fragments. The fission of U is predominantly binary, and may be exemplified by the following type of equation:

where x is a small number greater than unity.

Substantially all of the fission fragments have mass numbers within the range 77-158, although small quantities of isotopes of lower and higher mass numbers may result from unbalanced binary fission, ternaryfissiomor other reactions of infrequent occurrence. A very large majority of the fission fragments comprise a light group of mass numbers 84-106 and a heavy group of mass numbers 128-150.

The various fission fragmentsand the decay products.

of the initial fission fragments are referred to herein as fission products. These fission products fall within] a range of atomic numbers from about 32 to about 64. The fission products from the light group of fragments referred to above have atomic numbers ranging from about 35 to about 46; and the fission products fromthe heaw group of fragments have atomic numbers ranging from about 51 to about 60.

The various radioactive fission products have half lives ranging from a fraction of a second to thousands of years. Those having very shorthalf-lives may be eliminated by aging the material for a reasonableperiod before handling. Those with very long half-lives do 'not have 'sufiiciently intense radiation to protected by moderate shielding. the fission products having half-lives ranging from a few days to a few years have dangerously intense radiations which cannot be eliminated by aging for practical storage periods. These products are chiefly radioactive isotopes of Sr, Y, Zr, Cb, and Ru of the light group and Te, I, Cs, Ba, La, Ce and Pr of the heavy group.

The total amount of 93 and 94 produced from U in natural uranium by neutron bombardment is a function of neutron density and of the time of bombardment. Since 94 is fissionable under the conditions for fission of U the net yield of 94 per unit of time will decrease as the ratio of U content to 94 content of the mass decreases. For this reason, a neutronic reaction for 94 production is suitably terminated when only a fraction of the U has been converted to fission products. The reaction mass at this point contains a large amountof U a much smaller amount of U still smaller amounts of 93 94' and fission products, and traces of other products such as UX and UX By aging such a mass for a suitable period of time, the 93 may be substantially completely converted to 94 with simultaneendan'ger personnel On the other hand,

diifet'eht chemical composition. especially valuable in this respect and is superior to most .ous conversion of the short-lived radioactive fission products to longer-lived or stable isotopes.

The plutonium content of the aged reaction mass Will i usually be considerably less than 1% of the weight-of the unreacted uranium, and may even be less than one part by weight per-million parts byjweightof uranium. The

concentration of-"fission;- products will be of' the js'arne v order:ofY-ihagiiitude. The separation of -plutonium from such a'- mass involves extraction from the unreacted ated material to tively pure'plutonium c nd can be directly covered. a l

' Aniobject of the present invention is' to provide a new ean s'. for'separating plutonium from' and improved In aqueous media, particularly those which contain neutron v irradiated uranium and in which the plutonium is present in low concentration. i V

Another object of this invention is to provide a process of extracting plutonium from solutions of neutron irradiated uranium by the use of a normally solid insoluble phosphate as a carrier for that element.

A further object is to provide a method of extracting plutonium from solutions of neutron irradiated uranium by the use of the aforesaid phosphate carrier together with the subsequent utilization of another plutonium carrier having a different chemical composition.

A still further object of this invention is to provide a multistage multi-carrier process for the separation of plutonium from mixtures of plutonium and contaminating elements. I I Another object of the present invention is. to provide a process for alternately removing plutonium byfthe use of carriers of different chemical composition. whereby the plutonium is concentrated with respect to its carrier;

Still another object is to provide a process for'ooncentrating transuranic elements in solutions so dilute as to make impracticalthe direct removal of a precipitate consisting solely of insoluble compounds of said transuranic elements. V V I Plutonium exists in at least four states ofoxidation, i.e., +3, +4, +5, +6, and such valent states arejassociated with various degrees of stability',',the pentavalent state being the most unstable. V

'In accordance with'the present invention it has been discovered that plutonium when i'n' a valent state not greater than +4, preferably in the tetravalent state, can;

be readily carried from, solutions thereof asa phosphate by the use of a normally solid insoluble phosphate carrier or a combination of-the latter with a second carrier of Bismuth phosphate isother phosphates for thispurpose.

The-removal of plutonium from aqueous media as herein contemplated is extremely effective and substanstantial concentrations of fission products also are associated with the bismuth phosphate and are removed thereby. Consequently, where a solution of neutron irradiated uranium is contacted with the insoluble phosphate herein described, a substantial portion of the fission products are carried from the-solution with the plutonium. These fission products may be separated from the plutonium by forming an aqueous solution thereof and carrying or adsorbing the fissibh products from the solution .while maintaining the plutonium in .a valent. state. above +4,- preferably in the hexayalentfstatea Then-the pluto niuin maybe separat'fed; froiri ute adioaeuve. fission prod- I ucts by contaeting an aqueous solution containing 'pluto tially complete removal of the plutonium may be secured even though theplutonium concentration in the solution may be so low as to be well below the solubility of plutonium phosphate. Following removal of the plutonium a from solution, the plutonium may be recovered from the.

normally insoluble phosphates with which it is associated by various convenient methods. For example, the phosphates may be dissolved in nitric acid or similar acid and the solution extracted with a solvent for plutonium such as ethyl ether, hexone, etc., as described in co-pending application of Glenn T. Seaborg, Serial No 591,410, filed May 1, 1945. Alternatively plutonium maybeselectively adsorbed after dissolution in nitric acid by means ofa base. exchange adsorbent such as synthetic or natural zeolites as described in a'copending application'or' George E. Boyd, Serial No. 549,477, filed August 14, 1944, now US. Patent No. 2,849,282, issuedv August 26, 1958.

Concurrently with precipitation. or removal. of pluto nium by bismuth phosphate or similar phosphate subnium .itsplutonyl;state andfifission .products with a carrier, capable {of vfcafrryingf plutonium i-n; its tetravalent state or .with ab'aseex hangeadsorbentsuch as.I -R resins or natural zeolites or other agents described in the abovementioned' applicatiohioi GeorgeTBoyd-I v Various modifications. involving the above process of carrying plutonium are contemplated and where the plutonium is in low concentration or is contaminated with fission products the purification and[ or concentration may be'conducted in a. series of steps. In accordance with one modification of this invention; plutonium having a valent state not greater than +4 is carried from an aqueous solution by means of the insoluble 'phosphate'herein described. The insoluble phosphate and its associated plutonium are then dissolved to form a second aqueous solution. and the above cycle repeated in order to further decontaminate the .plutonium'with respect to uranium and certain more soluble fission products, or, preferablyusing a second carrier in the second cycle which differs in chernicalcornposition from the previous phosphate carrier used is employed .to efiecta further decontamination of plutonium with respect to the abovecontamination"lover1that obtainable from the successive use of the same plutonium carrier. Thus, in the decontaminationof plutonium ,withrespect'to uranium fission products,,t he use of a plurality of plutonium carriers which are noneis'omorphic with pluto 'um will permit a plurality of different isomorphic series of fission, products to.-be separated with thejdifierent supernatant. solutions. In this connection it shouldbe pointed out that the term "isomorphic". as usedlherein with respect to a'carrier of plutoniumrefer's to affco'mpound having a crystalline structurewith cation spacing in the crystallattice such that plutonium .o'rfother fcations mayjbe substituted the lattice for canrier cations. .7 f

The1alternate'usef of;difif-erent plutonium carriers also facilitates the concentrationjof plutonium with respect to its carrier; Theiratio. of carrier to plutonium'may be successively decreased in each cycle' of the process. Each carrier maybe dissolvedin ,a 'smallerfvolume' of solution than that requiredifor the preceding carrier; and a solution .may .finally-beLobtainedfromwhich a plutonium compound may be precipitated without'any carrier; Such concentration may beeffected simultaneously with decontamination, as in the recovery of plutonium from solutions or precipitates containing uranium. fission products. Alternatively, the. concentration may be applied to prevously decontaminated solutions or carrier precipitates, or for. the recoveryof plutonium. from dilutewaste solutions,.or the-like- Thesuccessive carriersin the present. process may difier in cations or in anions I or in both, and the cations may 7 i In. any case, however; the conditions for .the precipitation Ora subsequent carrier should be such thatat leastone of the ions oi the preceding carrier remains insoiuti'on. Since reduction; in carrier ratio in successive cycles is difficultinthe. case of common cations,1.'or;.common'cation elements, it is desirable to employ successive carriers having different cation metals, and it has been found preferable to employ combinations of carriers which differ both in cations and in anions. The following are examples of suitable carrier combinations:

With respect to the type of carriers to be employed subsequent to the use of the insoluble phosphate carrier, it is to be pointed out that such carriers as referred to herein and in the appended claims constitute a group of substantially insoluble solid finely divided compounds capable of ionizing to yield at least one inorganic cation and to yield at least one anion which constitutes an ionic component of a compound which is substantially more soluble than said finely divided compound and which contains the ion (plutonium ion in the present instance) to be carried. The preferred carriers for trivalent plutonium comprise compounds having an anion which is capable of forming an insoluble compound of trivalent cerium in the same solution; and the preferred carriers for tetravalent, plutonium comprise compounds having an anion which is capable of forming an insoluble compound of tetravalent cerium in the same solution.

Although the carriers may be employed as pre-formed finely divided solids, it is preferable to precipitate the carrier in situ since the latter procedure usually permits a'lower carrier ratio and results in more quantitative carrying of plutonium. In general, it is desirable to incorporate the carrier cation in the solution, agitate while adding the carrier anion, and digest the resulting mixture prior to separating the precipitate.

- Each precipitate is suitably dissolved in the minimum volume of solution from which the subsequent carrier may be precipitated substantially free from the preceding carrier. The use of different aqueous solutions of different composition (diiferent acidity, etc.), in succeeding stages will facilitate volume reduction, but the same solvent may be used if the concentrations are suitably adjusted. It is generally preferred to employ aqueous solvents and to modify their solvent power from stage to stage by adjustment of ionic concentrations. Thus, an aqueous solution of an inorganic acid or base may be used as the solvent in successive stages of the present process and the pH may be adjusted to increase the solvent power from stage to stage. Also, precipitation of a carrier in the presence of a large excess of one of the carrier ions will permit redissolving in a smaller volume of the same solvent in the absence of such excess ion. Alternatively, an additional ion may be introduced to form a soluble complex with the cation of the preceding carrier. Other equivalent. procedures for reducing the volume of solution from stage to stage and for precipitating a carrier free from preceding carrier will be evident to those skilled in the art.

The ratio of carrier to plutonium in the present process may vary over a wide range depending on the plutonium concentration of the original solution and upon the effectiveness of the particular carrier employed. Ratios raging from 10,000/1 or higher in the first stage of the process to /1 or lower in the final stage may be used. However, the ratio will generally fall within the range of 1,000/1 to 100/1. In the final carrier precipitation a relatively low ratio of carrier to plutonium is desirable, and in such case an isomorphic carrier is preferred.

After one or more carrier precipitations in accordance with the present concentration procedure, a final precipitation may be made with a sufficiently low ratio. of

carrier toplutonium so that the precipitate may be dissolved in a small volume of solution and a plutonium compound may then be precipitated directly without a carrier. If an isomorphic carrier is employed in the final carrier stage of the process, it will'be necessary to change the valence state of the plutonium, or of the carr-ier cation, in the final solution in order-to make a final precipitation of a plutonium compound free from carrier. On the other hand, if the final carrier is non-isomorphic with plutonium it will only be necessary to select conditions for the final precipitation of the plutonium compound such that at least the cation of the carrier remains in solution.

While the process of the present invention has been discussed in particular detail with respect to the utilization of the combination of a normally solid insoluble phosphate plutonium carrier together with a second plutonium carrier of different chemical composition, it is to be specifically understood that plutonium may be recovered in excellent yield by the use of only a normally solid insoluble phosphate carrier.

In accordance with a suitable method of effecting the separation of plutonium herein contemplated, the neutron irradiated uranium is dissolved in a suitable acid, such as for example nitric acid, to form uranyl nitrate and nitrates of plutonium, neptunium and the various fission products. Thereafter, sulfuric acid is added to the resulting solution and the acidity adjusted to a concentration of about 1 N with respect to sulfuric acid. The concentration of uranyl nitrate is also preferably regulated such that it is below about 22 percent by weight in order to keep the loss of plutonium at a minimum. Bismuth nitrate or another suitable compound which furnishes Bi+ ions is then added to the solution to produce a concentration of Bi+ ions of about 25 mg./ 10 cc. of solution. Phosphoric acid is next added to the solution in an amount such as to precipitate the bismuth and plutonium in the form of their phosphates. The concentration of Bi may be varied quite widely and with sulfuric acid a concentration of 10 mg. of Bi+ 10 cc. of solution will precipitate bismuth phosphate carrying plutonium without appreciable loss. A suitable concentration of phosphoric acid for solutions such as described above is about 0.36 M. The total acid concentration should be such that the uranyl phosphate formed will not precipitate; however, the concentration of acid in the solution should be such that the bismuth phosphate and plutonium phosphate precipitate together An acid concentration on the basis of added sulfuric or nitric acids of about 1 N has been found suitable. Below an acid concentration of about 0.85 N the precipitation of uranyl phosphate is initiated and above approximately 1.25 N, on the basis of added acid, the complete precipitation of bismuth phosphate and plutonium phosphate does not occur.

The use of sulfuric acid is preferable to nitric acid for adjusting the acidity since the possible precipitation of uranyl phosphate is further prevented by formation of complex ions or unassociated molecules by sulfate and uranyl ions. A source of sulfate ions other than sulfuric acid such as, for example, sodium sulfate can be used for this purpose.

In carrying out the above procedure the solutions are generally preferably heated to a temperature of, for example, about 70 C., until precipitation of the bismuth phosphate and plutonium phosphate appears to be substantially complete. In this connection, when working with solutions of neutron irradiated uranium which have not been sufiiciently aged, the bismuch phosphate will also carry down with it a portion of neptunium phosphate.

Inasmuch as the class of carriers employed in performing the process of the present invention does not carry neptunium or plutonium when these elements are in a valent state above +4, precautions should be taken prior to the *carryingstep to provide conditions such that the aforesaid elements are presentin'a state of oxidation not above +4. 'IThis pre'cautioniis especially desirable tuinstarices' Whereiheheutrori irradiate metal has been dissolved'and digested in nitric acid, since. under such conditions; the. plutonium Land/r neutunium is at least partially oxidized. tothe hexava'lent state. Suitable reduc ing: agents for' converting these elements from the'hexavalent state to thetetravalent state are hydroxylamina l ydrogen peroxide, sulfur.dioxide,-and'thelike.

- As examples of suitable normally'solid insoluble phosphates that may befemployed incarrying out the process of the present invention there may bementioned the phosphates of cerium (trivalent), bismuth, zirconium, and lanthanum.

The present invention may be further illustrated by the following specific examples.

EXAMPLE 1 A 20 percent uranyl nitrate solution 1 N nitric acid and containing 25 mg. Bi+ /l0 cc. was prepared. To small volumes (100, 10, or 1 10- cc.) of such solution were added appropriate quantities of Pu+ in the form of the nitrate toobtain the desired Bi Pu ratio. Thereafter sufficient 3.6 M phosphoric acid was added to render the resulting solutions 0.36 M with respect to phosphoric acid. The'solutions were next heated at 90 C. for about 45 minutes and then centrifuged. Aliquots of the supernatantliquid were analyzed for alpha radiation by means of standardcounter tube techniques. The precipitates which consisted essentiallyof a composition comprising bismuth and plutonium phosphates were washed three timesiwith 0.04 cc. of 3.6 M phosphoric acid, dissolved in hydrochloric acid and transferred to platinum dishes for alpha counting in accordance with the method referred to above. The plutonium in the aliquots of the supernatant liquids was separated from uranium by forming a precipitate of lanthanum fluoride which carried the plutonium down with it. Results of the experiments are summarizedin the table below.

Table I Activity recovered Activity recovered in the supernatant in the bismuth Percent Ratio BlzPu solution I (Counts phosphate precipi- 94pmper minute) tote (Counts per cipitated minute) 7 130 11, 920 1 cs. 9 92 6,300 98. 2 13, 800 99. 4 184 12, 500 98. 5 12 744 98. 4 150,000t1 6 134 95. 5

1 These counts'are corrected for a uranium blank by subtracting 18 counts per minute obtained by precipitating 4x101 grams of La as the fluoride in the presence of uranyl nitrate containing no Pu.

The concentration of Pu in this experiment was such as to probably exceed the solubility of plutonium phosphate in uranyl nitrate.

n EXAMPLE 2' Tetravalent plutonium hydroxide, prepared by neutralizing a nitric acid solution of plutonium nitrate with ammonium hydroxide,'is dissolved in 16 N nitric acid and the resulting solution is diluted to 1.0'N nitric acid after which the solution is saturated with sulfur dioxide. Orthophosphoric acid'is then added in an amount sufficient to produce a solution 0.6 M in orthophosphoric acid and 1.0 N in nitric acid. crystalline precipitatae conforms to the empirical formula PUPO4XH20. It is soluble in a 0.6 M orthophosphoric acid-1.0 N nitric acid solution to the extent of about 28 mg. plutonium per liter. The crystallinestructure of this compound is hexagonal with three molecules per unit The. lattice constants are:

a =6-.985-J :0.010\A.

Thecalculated density is 6.04.- l 1 shell.

The resulting violet colored tages are especially apparent insofar as reduction-in do:

contamination and. volume concentration factors are concerned. 7 I i EXAMPLEBK Neutron irradiated uranium'in the amount of 9 37 lbs; which had been aged in water'forv thirty-seven daysafter having bcenfsubjected to neutron bombardment at a power level of 250 mw. for one hundred days, is dissolved in Sumatra 60% nitriclacid to produce a solution containing 1.45 lbscof nitric acid per pound of uranium. Solutionis carried out at 100-1l5 C. until thenitric acid concentration is such that dilution to uranium nitrate hexahydrate will result in a solution 0.9 N' in nitric acid. The'volume'of this solution is'3,l23 gals, and its beta activity is approximately 2.5 l0 curies per /3 ton of uranium. The uranium concentrationof this solution is about 0.3 lb. per gal. and plutonium .ispresent as plutonous ion (+4) in a concentration of 0.0003 lb. per gal. To'this solution there is added sufiicient sulfuric acid to provide a concentration of the latter therein of the order of 0.204' lb. of sulfuric acid per lb. of uranium nitrate hexahydrate. This solution is next diluted with 'water so that the concentration of uranium nitrate hexahydrate is about 20% after thebismuth'phosphate'precipitation step outlined below. The temperature is then adjusted to about 40 C. after which aflsufficient quantity of a solution of sodium nitrite is added to render the resulting solution about 0.01 M therein. The temperature is now increased to around 75 C. and the mixture'permitted' to digest for a period of about one hour. Thereafter, there is added 39 gals. of a bismuth nitrate solution comprising 1.25 lbs. per gal. of bismuth (Bi in '10 N nitric acid, while agitating and maintaining a temperature of about 75 C. Approximately 138 gals. of 75% orthophospho'ric acid istlien added, with continued agitation, after which the mixture is digested at 75 C. for one hour. The bismuth phosphate-plutonous phosphate precipitate is then separated by'centrifuging and is washed with 20 gals. of an aqueous solution'containing 6.3% nitric acid and 2.9% orthophosphoric acid. The precipitate is next slurried with 275 gals. of 48% nitric acid, and the slurry is washed from the centrifuge with 20 gals. of water and agitated to dissolve the precipitate. The resulting solution has a volume of about 303 gals, and is approximately 9 N with respect to nitric acid. To the above solution there is added 45 gals. of an aqueous lanthanum nitrate solution containing approximately 2.2% La(No by weight (1% La The resulting solution is maintained at room temperature and agitated while adding 14.8 gals. of anhydrous hydrofluoric acid, and is then digested at a ternperature not substantially above C. forone-half hour. The lanthanum fiuoride-plutonous fiuoride precipitate is then separated by centrifuging and is washed with'water. The fluoride precipitate is next treated with 6 gals. of sodium hydroxide solution, agitating the' mixture for one-half hour at 5060- C. An additional 6 gals. of 40% sodium hydroxide solution is then added and the agita- 'tion is continued for another half-hour at SOL- C. The supernatant solution 'is 7 then separated and the La(=OH) -Pu(OH) mixture is thoroughly washed with water to remove residual sodium hydroxide and sodium fluoride. The'hydrated hydroxides are then dissolved in I about 2 gals. of 30% nitric acid to produce a solution having a volume of about 8 gals. The volume concentrati'on factor of the above process is about 390, and the carrier ratio concentration factor is about 960; The beta activity of the solution thus obtained is only 2% of the activity of the original solution, while the gamma activity thereof is decreased by the same order of. magnitude. The final solution'h'as a1 plutonium concentration sufficiently high to permit direct precipitation of plutonium peroxide, or other insoluble plutonium compound, Without the co-precipitation of a carrier.

While the present invention has been described With particular emphasis on the use of bismuth phosphate in the modifications of the present invention discussed above, it will be readily apparent to those skilled in the art that other normally solid insoluble phosphates, some or" which have been mentioned heretofore, are capable of functioning as satisfactory equivalents of bismuth phosphate. Hence, the utilization of any such phosphate in accord ance with the general procedure set forth above will be considered as falling within the scope of the present invention.

Likewise, it will be understood, of course, that the above examples a e merely illustrative and do not in any way limit the scope of this invention. Numerous combinations of carriers other than those of the specific examples may be employed; and more than two different carriers may be used, or two different carriers may be used successively in a plurality of cycles. Various modifications of the procedures employed in the examples will also be apparent to those skilled in the art.

Although the present invention has been illustrated with particular reference to the concentration of plutonium in dilute solutions, and is especially useful for this purpose, it should be understood that this invention is equally applicable to the concentration of neptunium or of mixtures of neptunium and plutonium. All of the procedures disclosed above may be applied to dilute solutions of neptunium, or to dilute solutions or neptunium and plutonium, as well as to aged solutions containing only plutonium.

In general, it may be said that the use of any equivalents or modification of procedure which would naturally occur to those skilled in the art is included in the scope of the present invention. Only such limitations should be imposed on the scope of this invention as are indicated in the appended claims.

This is a continuation-in-part of co-pending application U.S. No. 478,570, filed March 9, 1943, now U.S. Patent No. 2,799,553, issued July 16, 1957, and all subject matter therein not inconsistent with the subject matter herein is incorporated in the present disclosure by reference.

What is claimed is: a

1. In a process for the concentration of plutonium in a dilute aqueous solution of nitric acid containing plutonous ion, the steps which comprise incorporating in said solution bismuthnitrate and orthophosphoric acid, separating from the supernatant solution the resulting bismuth phosphate-plutonous phosphate precipitate, dissolving said phosphate precipitate in aqueous nitric acid to form a second solution of substantially smaller volume than said first solution, incorporating in said second solution lanthanum nitrate and hydrofluoric acid, and separating from the supernatant solution the resulting lanthanum fluoride-plutonous fluoride precipitate.

2. In a process for the concentration of plutonium in a dilute aqueous solution of nitric acid containing plutonous ion, the steps which comprise incorporating in said solution bismuth nitrate and orthophosphoric acid, separating from the supernatant solution the resulting bismuth phosphate-plutonous phosphate precipitate, dissolving said phosphate precipitate in aqueous nitric acid to form a second solution of substantially smaller volume than said first solution, incorporating in said second solution lanthanum nitrate and hydrofluoric acid, separating from the supernatant solution the resulting lanthanum fluoride-plutonous fluoride precipitate, transforming the fluorides in said precipitate to the corresponding hydroxides by agitating the precipitate in a solution of sodium hydroxide, dissolving said hydroxides in an aqueous solution of an inorganic acid to form a third solution having a substantially smaller volume than said second solution, incorporating in said third solution an anion which forms an insoluble compound with plutonous ion and a soluble compound with lanthanum ion, and separating the resulting plutonous compound from the supernatant solution.

.3. In a process for the concentration of plutonium in a dilute nitric acid solution containing impurities commonly associated therewith and plutonium in a valent state not greater than +4, the steps which comprise in corporating bismuth phosphate in said solution, separating from the supernatant solution said phosphate together with the plutonium, dissolving this precipitate in aqueous nitric acid to form a second solution containing plutonium in a valent state not greater than +4, incorporating in the resulting solution a plutonium carrier selected from the group consisting of lanthanum fluoride, uranium acetate, bismuth hydroxide, and columbic oxide, and separating the second carrier and its associated plutonium from the supernatant solution.

4. A process for separating contaminants from plutonium which is in an aqueous inorganic acid solution containing plutonium ions in an oxidation state not greater than +4 and cations of contaminating elements comprising, incorporating bismuth phosphate as carrier for the plutonium in said solution, separating the precipitate and its associated plutonium from the supernatant solution, dissolving said precipitate and its associated plutonium in an aqueous inorganic acid to form a second solution containing plutonium in a valent state not greater than +4, incorporating in said second solution a quantity of a second carrier for plutonium substantially less than the quantity of said first carrier, said second carrier being selected from the group consisting of lanthanum fluoride, uranium acetate, bismuth hydroxide, and columbic oxide, separating the second carrier precipitate and its associated plutonium from the supernatant solution, and dissolving the second precipitate and its associated plutonium to form a third aqueous inorganic acid solution of substantial] less volume, than the said firstsolution.

5. The method of separating plutonium from substances 7 present in neutron irradiated uranium, which comprises H dissolving said neutron irradiated material in nitric acid adding a reducing agent capable of reducing plutonium to a valence state not greater than +4, adjusting the concentration of the uranyl nitrate thus formed to about 22%, adding sulfuric acid to a concentration of about 0.85 to 1.25 N based on the nitric and sulfuric acids present, adding a soluble bismuth compound and a soluble phosphate and precipitating bismuth phosphate, thereby carrying plutonium out of solution, dissolving the resultant phosphate precipitate in aqueous nitric acid to form a second solution containing plutonium in a valent state not greater than +4, incorporating in said solution a plutonium carrier selected from the group consisting of lanthanum fluoride, uraniumacetate, bismuth hydroxide, and columbic oxide, and separating said second carrier and its associated plutonium from the supernatant solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,799,553 Thompson et a1. July 16, 1957 

1. IN A PROCESS FOR THE CONCENTRATION OF PLUTONIUM IN A DILUTE AQUEOUS SOLUTION OF NITRIC ACID CONTAINING PLUTONOUS ION, THE STEPS WHICH COMPRISE INCORPORATING IN SAID SOLUTION BISMUTH NITRATE AND ORTHOPHOSPHORIC ACID, SEPARATING FROM THE SUPERNATANT SOLUTION THE RESULTING BISMUTH PHOSPHATE-PLUTONOUS PHOSPHATE PRECIPITATE, DISSOLVING SAID PHOSPHATE PRECIPITATE IN AQUEOUS NITRIC ACID TO FORM A SECOND SOLUTION OF SUBSTANTIALLY SMALLER VOLUME THAN SAID FIRST SOLUTION, INCORPORATING IN SAID SECOND SOLUTION LANTHANUM NITRATE AND HYDROFLUORIC ACID, AND SEPARATING FROM THE SUPERNATANT SOLUTION THE RESULTING LANTHANUM FLUORIDE-PLUTONOUS FLUORIDE PRECIPITATE. 